.TH std::bad_cast 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::bad_cast \- std::bad_cast

.SH Synopsis
   Defined in header <typeinfo>
   class bad_cast : public std::exception;

   An exception of this type is thrown when a dynamic_cast to a reference type fails
   the run-time check (e.g. because the types are not related by inheritance), and also
   from std::use_facet if the requested facet does not exist in the locale.

   std-bad cast-inheritance.svg

                                   Inheritance diagram

.SH Member functions

   constructor   constructs a new bad_cast object
                 \fI(public member function)\fP
   operator=     replaces the bad_cast object
                 \fI(public member function)\fP
   what          returns the explanatory string
                 \fI(public member function)\fP

std::bad_cast::bad_cast

   bad_cast() throw();                                 \fI(until C++11)\fP
   bad_cast() noexcept;                        \fB(1)\fP     \fI(since C++11)\fP
   bad_cast( const bad_cast& other ) throw();      \fB(2)\fP               \fI(until C++11)\fP
   bad_cast( const bad_cast& other ) noexcept;                       \fI(since C++11)\fP

   Constructs a new bad_cast object with an implementation-defined null-terminated byte
   string which is accessible through what().

   1) Default constructor.
   2) Copy constructor.
   If *this and other both have dynamic type std::bad_cast then std::strcmp(what(),
   other.what()) == 0.
   \fI(since C++11)\fP

.SH Parameters

   other - another exception object to copy

std::bad_cast::operator=

   bad_cast& operator=( const bad_cast& other ) throw();   \fI(until C++11)\fP
   bad_cast& operator=( const bad_cast& other ) noexcept;  \fI(since C++11)\fP

   Assigns the contents with those of other.
   If *this and other both have dynamic type std::bad_cast then std::strcmp(what(),
   other.what()) == 0 after assignment.
   \fI(since C++11)\fP

.SH Parameters

   other - another exception object to assign with

.SH Return value

   *this

std::bad_cast::what

   virtual const char* what() const throw();   \fI(until C++11)\fP
   virtual const char* what() const noexcept;  \fI(since C++11)\fP

   Returns the explanatory string.

.SH Parameters

   \fI(none)\fP

.SH Return value

   Pointer to a null-terminated string with explanatory information. The string is
   suitable for conversion and display as a std::wstring. The pointer is guaranteed to
   be valid at least until the exception object from which it is obtained is destroyed,
   or until a non-const member function (e.g. copy assignment operator) on the
   exception object is called.

.SH Notes

   Implementations are allowed but not required to override what().

Inherited from std::exception

.SH Member functions

   destructor   destroys the exception object
   \fB[virtual]\fP    \fI(virtual public member function of std::exception)\fP
   what         returns an explanatory string
   \fB[virtual]\fP    \fI(virtual public member function of std::exception)\fP

.SH Example


// Run this code

 #include <iostream>
 #include <typeinfo>

 struct Foo { virtual ~Foo() {} };
 struct Bar { virtual ~Bar() { std::cout << "~Bar\\n"; } };
 struct Pub : Bar { ~Pub() override { std::cout << "~Pub\\n"; } };

 int main()
 {
     Pub pub;
     try
     {
         [[maybe_unused]]
         Bar& r1 = dynamic_cast<Bar&>(pub); // OK, upcast

         [[maybe_unused]]
         Foo& r2 = dynamic_cast<Foo&>(pub); // throws
     }
     catch (const std::bad_cast& e)
     {
         std::cout << "e.what(): " << e.what() << '\\n';
     }
 }

.SH Possible output:

 e.what(): std::bad_cast
 ~Pub
 ~Bar
